Thursday, September 13, 2012

Plastic Race Engines - Polimotor

Like a lot of the odd and awesome stuff one encounters on the internet, there's tanitalizingly little information available on the Polimotor. From what I can gather, there were at least three different engines developed using the technology. I'll start with the two that appear to be best-known.

"Designed and developed by Polimotor founder and president Matty Holzberg, the engine, based on a Cosworth BDA, tipped the scales at 168 lbs - half the weight of its metal counterpart. Plastic parts included the engine block, cam cover, air intake trumpets, intake valve stems, piston skirts and wrist pins, connecting rods, oil scraper piston rings, tappets, valve spring retainers and timing gears."

Illustrated below, and powering the Lola T616 pictured beneath, this iteration developed 320 HP at 9,500 RPM and ran reliably for two seasons of IMSA Camel GT Championship in 1984 and 1985. Here's a link to the quoted source.

Here's a Ford 2.3 version - it made 318 HP @ 11,000 RPM and redlined at 14,000. Popular Science further details it here. There seems to be some confusion as to whether these two are the same motor, as the articles linked above, in addition to this Wikipedia entry, contain contradictory information.

The following is quoted from an old Car Lounge thread, itself quoting a now-dead link:

"The engine used metal cylinder sleeves, metal combustion chamber tops, metal piston crowns, bearings, valves & seats, and a stock 2.3L Pinto crankshaft. Darn near everything else in the engine, including the block, conrods, piston skirts, etc. was fiber-reinforced plastic. The exact type of plastic escapes me at the moment. Very little metal was used outside of the crankshaft; just small/thin metal parts to shield against direct contact with combustion, and on mechanical wear surfaces.

This experimental engine was reportedly a great success, several were built and used very successfully in racing. HP & RPMs were dramatically higher than in the metal original, and it was quite smooth-running and durable and something like 1/3 the weight. The achilles heel was cost. The engines were practically hand-built and would have been very pricey in production compared to mass-produced metal engines. They tried but just couldn't scope out a way to mass-produce the plastic parts competitively, so Ford canned further research. When the few racing engines finally burned out, that was the end of it. However the developers noted that in limited production, the tooling and fabrication methods actually made it easier and cheaper to build than a limited-production metal engine (with small-batch custom castings, forgings, and machine jobs) - that is, for those with the unusual skills and knowledge needed. But virtually no engine shop would be able to handle such an exotic project, which is probably why it was never duplicated to my knowledge. Weird stuff like fiber orientation for load transfer, resin/fiber ratios, resin wetting, layup, mold closing, bubble exclusion, mold-integrated component positioning jigs, etc. are as incomprehensible as quantum physics or UFO engineering to most 20th/early21st century engine builders, trained, experienced, and focused as they are on metalworking. Some engine shops might know a surfboard builder, EAA guy, or body wizard who can whip up custom carbon/epoxy valve covers or oil pans for them, but that is about all, high-load polymer working parts get pretty freaky, and the idea is so obscure that it just never pops up in the first place. If they want exotic structural or loaded stuff, they'll go with CNC'd alloy billet and feel pretty daring about it. The plastic engine was (and still is) just way too far ahead of its time. Pretty amazing that it was built in the mid-1980s.

It was also noted that the crankshaft could have been made of fiber-reinforced polymer with thin metal journal inserts, which would have upped rpms/hp even more and saved a bunch more weight, but they stuck with the stock metal crank because of budget & time limitations. They were really pushing the technological envelope as it was."

The third, and perhaps most interesting of the Polimotors, is the turbo V6. It seems to have been developed for Indy racing, but I don't believe it ever ran in competition - I'm sure there'd be more details available if it had.

I'm utterly intrigued by all this, and frustratingly left with more questions than answers - though in some perverse way, the mystery makes it that much more satisfying. I hope your mind is blown even half as much as mine was.

2 comments:

with car builders, perhaps not engine builders though, now far more skilled with carbon fibre and kevlar etc. I wonder if a new non-metal engine could be imagined. Seems to me that something carbon based would withstand heat better, assuming the resin used could also.